If you’ve got a burn, the time of day you were injured might impact how long it takes your skin to heal, according to new research on the circadian rhythms of our skin cells.

STAT chatted with study author and cell biologist John O’Neill of MRC Laboratory of Molecular Biology about the work, published in Science Translational Medicine.

What do we know about the biological clock of skin cells?

We’ve known for years that the biological clock is in every single cell of the body. I could scrape your cells, put them in a dish, and they would continue to show daily rhythms. We looked at fibroblasts, skins cells that are really important in repairing wounds. We found that the major class of proteins that was changing over time were proteins that have to do with cell movement and the cytoskeleton. Because we saw this rhythm in the cytoskeleton, particularly in fibroblasts, we predicted that the time of day biologically when a wound happens would make a big difference in how well that wound heals, because the fibroblast needs to move into that wound to repair it.

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What did you see happening with the fibroblasts?

That’s exactly what we found in isolated cells in the lab, in slices of skin, and in mouse models. What we saw at every level was this control of the cellular clock was leading to really clear time-of-day effect in how quickly fibroblasts move into the wound. We consistently saw about a twofold difference in the effects between day and night, which is really big really for something like this. It’s one thing observing a big effect in individual cells, but when it shows such a big effect in mice, it starts to raise your eyebrows.

What was your next step?

We connected with colleagues who had a database on recovery after burn wounds. We saw almost a twofold difference depending on the time of day — people injured during the day took 17 days to heal, compared to 28 days on average for those injured at night. Of course we can’t say the movement of skin cells is the only thing that contributes to this time-of-day effect, but it certainly seems to be a contributor.